Pixel sensor cells as well as other CMOS devices have sensitive components that require some degree of shielding in order to reduce, e.g., noise. For example, in pixel sensor cells, active pixel sensor cells include photodiodes combined with a number of active transistors which, in addition to forming an electrical signal, provide amplification, readout control, and reset control. However, stray light can strike sensitive areas of the active transistors, storage areas, etc. resulting in unwanted noise.
To control this noise, CMOS processes require metal lines to be formed in upper back end of the line metal layers, located above the active transistors, storage areas, etc. These metal lines shield sensitive regions from light, which would otherwise be absorbed causing degraded performance through mechanisms such as color crosstalk, smear, or reduced blooming control. Obviously, this is undesirable.
However, many issues exist. By way of example, the formation of the metal wires require additional, expensive metal fabrication processes. Also, these metal lines are formed on upper metal wiring layers, which require considerable space, thereby reducing the space for other critical components, wires, interconnects, etc. For example, in currently available CMOS fabrication processes, the transistors are formed at a first level and the metal lines are formed at upper metal wiring levels. However, these upper levels are typically used for back end of the line components. Also, as the metal lines are formed in these upper layers, incident or stray light can still strike sensitive areas, resulting in noise and hence performance degradation.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.